Short-arc electric discharge lamp having an arc-ignitor assembly that is movably mounted within an integral part of the lamp envelope

ABSTRACT

A SHORT-ARC DISCHARGE LAMP IS STARTED ON ITS OPERATING VOLTAGE SUPPLY BY AN ARC-IGNITOR ASSEMBLY THAT IS MOVABLY MOUNTED WITHIN A SEALED LATERALLY-EXTENDING HOLLOW ARM PROVIDED ON THE ENVELOPE AND, WHEN ACTUATED, BRIDGES THE DISCHARGE GAP BETWEEN THE ELECTRODES AND IS THEN WITHDRAWN FROM SUCH POSITION. IN ONE EMBODIMENT THE IGNITOR ASSEMBLY COMPRISES A MECHANICALLY ACTUATED LEVER THAT IS PIVOTALLY MOUNTED IN THE ENVELOPE ARM AND IS MOVABLY SEALED THERETO BY A SYLPHON BELLOWS. IN ANOTHER EMBODIMENT THE IGNITOR ASSEMBLY IS RECIPROCALLY MOVABLE WITHIN THE SEALED ENVELOPE ARM AND INCLUDES AN IRON ARMATURE THAT IS MAGNETICALY ACTUATED BY AN EXTERIOR ELECTROMAGNET MOUNTED ON THE ARM.

United States Patent 1 Inventor Norman C. Beese Verona, N-J.

Appl. No. 768,453

Filed Oct. 17, 1968 Patented June 28, 1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

SHORT-ARC ELECTRIC DISCHARGE LAMP HAVING AN ARC-IGNITOR ASSEMBLY THAT IS MOVABLY MOUNTED WITHIN AN INTEGRAL PART OF THE LAMP ENVELOPE 8 Claims, 2 Drawing Figs.

U.S. Cl 313/146, 313/152, 313/162, 315/331 lnLCl H0lj 7/36, l-lOlj 61/54 Field of Search 313/48,

Primary Examiner- Roy Lake Assistant Examiner-E. R. La Roche AnomeysA. T. Stratton, W. D. Palmer and D. S. Buleza ABSTRACT: A short-arc discharge lamp is started on its operating voltage supply by an arc-ignitor assembly that is movably mounted within a sealed laterally-extending hollow arm provided on the envelope and, when actuated, bridges the discharge gap between the electrodes and is then withdrawn from such position. In one embodiment the ignitor assembly comprises a mechanically actuated lever that is pivotally mounted in the envelope arm and is movably sealed thereto by a sylphon bellows. ln another embodiment the ignitor assembly is reciprocally movable within the sealed envelope arm and includes an iron annature that is magnetically actuated by an exterior electromagnet mounted on the arm.

SHORT-ARC ELECTRIC DISCHARGE LAMP HAVING AN ARC-IGNITOR ASSEMBLY THAT IS MOVABLY MOUNTED WITHIN AN INTEGRAL PART OF THE LAMP ENVELOPE BACKGROUND OF THE INVENTION This invention relates to electric discharge devices and has particular reference to an improved short-arc discharge lamp having means which facilitates the starting of the lamp and is incorporated as an integral part of the lamp envelope.

Short-arc high-intensity lamps are well known in the art and require rather elaborate and expensive starting circuits by virtue of the fact that a much higher voltage is required to strike the are between the electrodes than to operate the lamp after it has been started. A typical lamp of this type requires starting voltages in the order of to 40 kilovolts even though the operating voltage is in the order of 20 volts. For this reason, various types of auxiliary or starting electrodes and devices have been developed to ignite the arc and lower the starting voltage.

A discharge lamp in which the arc is initiated by a member that temporarily bridges the discharge gap between the electrodes and is then held at a location remote from the electrodes by means of an armature and an exterior electromagnet that is connected in series with the electrodes, and is thus continuously energized during lamp operation, is disclosed in U.S. Pat. No. 1,551,524. A high-pressure arc lamp having a movable main electrode that initially is in contact with the other main electrode and is then pulled away from the latter by an electromagnet placed around the one end of the arc tube is disclosed in U.S. Pat. No. 2,156,369. Arc lamps in which the arc is struck by a movable main electrode that is attached to the lamp envelope by a flexible bellows assembly are also known and a lamp of this character is disclosed in U.S. Pat. No. 2,545,345.

While the prior art starting devices and arrangements did lower the starting voltage they were not entirely satisfactory since they employed movable main electrodes which complicated the design and manufacture of the lamp or required an electromagnet that was constantly energized and connected in series with the lamp electrodes and, thus, reduced the overall efficiency of the lamp.

It is accordingly thegeneral object of the present invention to provide a high-pressure electric discharge lamp that can be started on the same voltage supply on which it is operated and which can be readily and inexpensively manufactured.

Another and more specific object is the provision of a shortarc discharge lamp that eliminates the need for complicated and costly high-voltage starting circuits and which is of simple construction and able to withstand the vibration and mecha:ni cal shocks encountered during normal usage.

The foregoing objects and additional advantages are achieved in accordance with the present invention by mounting a movable arc-initiating assembly within a vitreous tubular appendage that laterally protrudes from and is hermetically sealed to the envelope wall. In accordance with one embodiment the starting assembly comprises a rigid lever that is movably and hermetically sealed to the envelope arm by a sylphon bellows and extends beyond the outer end of the envelope arm. The lever extends through and pivots about an apertured disc secured to the envelope arm and carries a refractory metal ignitor bar at its inner end which makes-andbreaks contact with both of the electrodes when the outer end of the lever is manipulated.

In another embodiment the ignitor assembly is actuated magnetically rather than mechanically. According to this embodiment the ignitor bar is secured to an iron armature that is located within the envelope arm and is actuated by an exterior electromagnet (or a pair of electromagnets) which cause the armature to move toward and away from the electrodes and causes the ignitor bar to make-and-break contact with the tips of electrodes. The electromagnetic actuating means is energized by a separate voltage source or can be connected in parallel with the voltage source employed to operate the lamp. If two electromagnetic coils are used, and one of them remains energized during lamp operation to keep the ignitor in its retracted position, then a diaphragm of sheet iron is placed on the envelope arm between the electromagnets and the body portion of the envelope to shield the are from stray magnetic fields that may be generated by the electromagnets.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIG. 1 is a side sectional view of a short-arc discharge lamp embodying an integral arc-ignitor assembly adapted for mechanical actuation; and

FIG. 2 is a similar view of an alternative lamp embodiment having an arc-ignitor that is magnetically actuated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown a short-arc high-intensity lamp 10 which embodies one form of the invention and consists of a light-transmitting vitreous envelope 12 having a bulbous body portion that is terminated at each end by axially extending seal arms 14 and 15. The envelope is preferably made from a material, such as quartz, which will withstand the high operating temperatures which prevail in the lamp. The lamp 10 here illustrated is designed for operation on a direct-current voltage source and, accordingly, the envelope 12 contains an elongated cathode l6 and an enlarged elongated anode 17 that are spaced a predetermined distance apart and are anchored in the seal arms 14 and 15, respectively. The anode 17 is connected to a rigid outer conductor 18 through a plurality of foil conductors 20 that areembedded in the fused arm 15 of the envelope. The outer conductor 18 is, in turn, connected to a metal cap 22 that is secured to the end of the arm 15 and serves as one of the lamp terminals. The cathode 16 is similarly connected to a second terminal cap 24 that is mounted on theend of the arm 14.

The cathode 16 is also fitted with a quartz sleeve 21 that is fused to the envelope am 14 so that only the pointed inner end portion of the cathode is exposed.

In accordance with the present invention, the voltage required to start the lamp 10 is reduced by pivotally mounting an arc-ignitor assembly 29 in a sealed vitreous appendage such as a tubular arm 30 that is integral with the body portion of the envelope l2 and extends laterally therefrom. As shown, the tubular arm 30 is perpendicular to the longitudinal axis of the lamp l0 and is aligned with the discharge gap defined by the inner ends of the cathode 16 and anode 17.

The ignitor assembly 29 consists of an elongated rigid member such as a refractory metal rod 32 that extends from the tubular arm 30 into the body portion of the envelope l2 and has an enlarged ignitor bar 33 at its end that is conformed and positioned to slide across the end of the cathode l6 and abuttingly contact the end of the anode 17 when the rod is moved in the direction of the lamp axis, as shown by the phantom outline of the inner end of the rod 32 in FIG. 1. The refractory metal bar 33 thus shifts from a position behind the tip of the cathode 16 into contact with both electrodes and bridges the discharge gap therebetween.

The outer end of the rod 32 is rigidly connected to a second metal rod 34 that extends through a diaphragm 36 at the end of a sylphon bellows 37 that is hermetically sealed to the intumed flange of the arm 30 by a graded seal component 38 and a glass ring 40 that matches the expansion coefficient of the metal collar 42 on the outer end of the bellows 37 to which it is sealed. The inner end of the bellows 37 is provided with a spring-loaded cap 44 which is attached to the rod 32 and absorbs thermal expansions of the internal metallic components of the ignitor assembly 29. The cap 44 also compensates for changes in the length of the sylphon bellows 37 caused by pressure changes and thus keeps the ignitor bar 33 in contact with the cathode l6.

The conjoined rods 32 and 34 constitute a unitary rigid lever that is movable with respect to the envelope arm 30 and the fixed electrodes 16 and ll7. The rod 32 extends through an apertured disc 48 of molybdenum or other suitable metal that is embedded in the wall of the quartz arm 30 and is reinforced by washers 50 of fused quartz located on either side of the disc. The lever is thus pivoted about a point located between the inner end of the bellows 37 and the mouth of the arm 30 so that the ignitor bar 33 can be shifted into bridging-contacting relationship with both electrodes 16 and 17 by moving the protruding end of the rod 34 in the opposite direction, as shown by the phantom outline of the lever in FIG. 1.

The sylphon bellows 37 are made of metal and have sufficient flexibility to allow linear motion imparted to the lever external to the lamp to be transmitted to the ignitor bar 33 without rupturing the hermetic seal with the envelope arm 30. The linear motion or displacement of the protruding end of the lever can be applied manually or with suitable electromagnetic means or by a motor.

To start the lamp It the lever is first shifted to place the ignitor bar 33 in bridging relationship with the electrodes 16 and 117. The lamp is then connected to a suitable direct-current voltage source by conductors 26 and 27 which are connected to the terminals 24 and 22, respectively, through a switch 23. The lever is then shifted to withdraw the ignitor bar 33 away from the anode l7, thus drawing an are which immediately transfers to the pointed tip of the cathode 16. In the case of a xenon-filled short-arc lamp having an operating voltage of approximately volts, the aforesaid mechanically actuated ignitor assembly pennits the lamp to be started on its normal supply voltage 50 to 100 volts DC. The rod 32 and ignitor bar 33 are manufactured from tungsten or other suitable refractory metal. The resulting ignitor assembly provides reliable starting and will withstand vibration and mechanical shocks without damage or malfunctioning.

In FIG. 2 there is shown an alternative form of the invention wherein a short-arc lamp 10a of the same basic construction as that previously described is provided with a hermetically sealed tubular arm 30a that extends laterally from the bulbous body portion of the envelope 12a in a direction normal to the longitudinal axis of the lamp and is aligned with the discharge gap between the cathode 116a and anode 17a. The metal ignitor bar 33a in this case is attached to the end of a metal rod 52 that extends into the arm 30a and is connected to an armature 53 of suitable magnetically responsive material, such as iron, that is located in the outer end of the arm. The armature 53 is magnetically actuated by an electromagnet consisting of two independently energizable solenoids 41 and 43 that are mounted on and encircle the outer end ofthe arm 30a.

The ignitor bar 33a, rod 52, and armature 53 thus comprise an integral elongated assembly that is reciprocally movable within the hollow arm 30a along a path such that the ignitor bar can be placed in bridging and contacting relationship with the ends of the electrodes 16a and 17a and then can be withdrawn from such position, as indicated by the phantom showing of the armature and inner end of the rod depicted in FIG. 2.

The rod 52 is constrained to move toward and away from the discharge gap at the center of the envelope 120 by a suitable guide means such as a section of quartz tubing 31 that is sealed to the inner wall of a constricted section of the arm 30a that is located between the armature 53 and the body portion of the envelope 12a. A helical spring 46 attached to the outer end of the armature 53 maintains a spacing between the annature and walls of the arm 30a and thus cushions the armature both radially and longitudinally and permits the lamp 10a to withstand vibration and mechanical shocks without damage.

As shown in FIG. 2, the lamp ll'lla is connected to a suitable direct-current operating voltage source (not shown) through conductors 26a and 27a that are connected to the lamp terminals 22a and 24a through a main switch 23a. A suitable ballast resistor 35 is included in the supply line 27a to control the lamp current during operation. A suitable ballast resistor (not shown) is also desirably provided in the supply line 27 of the lamp W shown in FIG. I for the same purpose.

The solenoids 41 and 43 are connected across the operating voltage source in parallel with the lamp 10a by suitable conductors 45, 47, 511 and 52. The solenoids 41 and 43 are independently energizable and are controlled by a switch 54 that has a pair of contactors 56 and 57 which close and open the circuits to the respective solenoids. The switch 54 is spring-loaded, as shown, so that the circuit that supplies the solenoid 411 is normally closed and the circuit to the other solenoid 43 is normally open. Solenoid 41 will thus be continuously energized while the lamp is operating, whereas the other solenoid 43 will be energized only when the switch 54 is operated.

A variable resistor 49 is connected in series with the solenoids 41 and 43 by conductor 47 to permit a constant voltage to be applied to the solenoids and make the magnetic control circuit independent of the lamp characteristics.

Starting of the lamp 10a is thus achieved by momentarily closing the switch 54 and energizing the solenoid 43 and urging the armature 53, rod 52 and the ignitor bar 33a inwardly as a unit so that the bar contacts the electrodes 16a and 17a and bridges the discharge gap. The switch 54 is then released thus deenergizing solenoid 43 and energizing solenoid Ill-causing the bar 33a to be pulled away from the electrodes and initiating the are.

If the solenoids 411 and 43 are not shielded or located a sufficient distance from the electrodes 16a and 17a, the magnetic fields produced by the energized coils may cause the arc to become distorted or unstable. A diaphragm 58 of sheet iron or other suitable metal is thus placed on the envelope arm 30a at a location between the solenoids 41 and 43 and the body portion of the envelope 12a so as to shield the are from any such magnetic disturbances. A reflector 60 may also be mounted on the arm 30a between the magnetic shield 58 and bulbous body portion of the envelope 12a to direct the light rays in a particular direction, if desired.

If the lamp Ma is operated in a vertical position and is stationary, solenoid 41 may be deenergized as soon as the arc is ignited since the armature 53 and attached rod 52 and ignitor 33a will remain in their retracted positions. The magnetic shield 53 would then not be required. The same situation would prevail, of course, if the lamp were operated so that the tubular arm 30a were directed downwardly.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that a short-arc lamp having a simple, reliable and inexpensive integral arc-ignitor assembly has been provided.

While several embodiments have been illustrated and described, it will be understood that various modifications in the construction and arrangement of the assembled components can be made without departing from the spirit and scope of the invention.

I claim:

I. A short-arc electric discharge lamp comprising:

a sealed elongated vitreous envelope having (a) a bulbous body portion, (b) an integral hollow appendage that extends laterally from a medial part of said body portion, and (c) a sealed longitudinally extending arm at each end of said body portion;

a pair of spaced electrodes within the body portion of said envelope and anchored in the respective sealed arms so that said electrodes define a discharge gap of predetermined length which extends in the same direction as the longitudinal axis of said envelope;

a movable elongated ignitor assembly within and extending from said appendage into the body portion of said envelope and having an arc-ignitor component at its inner end that is disposed and conformed to bridge said discharge gap and make-and-break contact with said electrodes when said ignitor assembly is actuated so that the inner end thereof moves along a prescribed path toward and away from the discharge gap; and

means associated with and exterior to said envelope appendage for actuating said elongated ignitor assembly and moving the arc-ignitor component thereof along said path and into make-and-break contacting relationship with said electrodes.

2. The short-arc electric discharge lamp of claim 1 wherein:

said envelope appendage comprises a tubular vitreous arm;

and

said actuating means comprises (a) a sylphon bellows that is hermetically sealed to the outer end of the tubular am of said envelope, and (b) a rigid elongated member that ex tends through and is hermetically joined to said sylphon bellows and protrudes beyond the outer end of said tubular arm, said elongated ignitor assembly being fastened to the inner of said elongated member and constituting therewith a unitary rigid lever that is movable with respect to said lateral arm.

3. The short-arc electric discharge lamp of claim 2 wherein:

said lateral tubular arm is substantially normal to the longitudinal axis of said envelope;

said electrodes are arranged so that the discharge gap is in substantial alignment with said tubular arm; and

the inner end of said lever extends through an apertured disc that is secured to said tubular arm at a location between the inner end of said bellows and the mouth of said tubular arm and said lever is thus pivotally movable about said disc.

4. The short-arc electric discharge lamp of claim 3 wherein:

one of said electrodes comprises a cathode and the other of said electrodes comprises an enlarged anode;

said arc-ignitor component comprises a refractory metal bar secured to the inner end of said lever; and

said ignitor bar, when in break-contact position, is disposed behind the tip of said cathode and, when in make-contact position, is seated against the tips of said cathode and anode.

5. The short-arc electric discharge lamp of claim 1 wherein:

said envelope appendage comprises a tubular vitreous arm that is substantially normal to the longitudinal axis of said envelope and is closed at its outer end;

said actuating means comprises (a) an armature of magnetically responsive material that is secured to the outermost end of said movable ignitor assembly and is located within the laterally extending arm of said envelope and (b) an exterior electromagnet that is disposed in encircling relationship with said tubular arm of the envelope; and

said armature and ignitor assembly being reciprocally movable with respect to said tubular arm along a path such that the arc-ignitor component makes-and-breaks contact with both of said electrodes in response to the movement of said armature.

6. The short-arc electric discharge lamp of claim 5 wherein said electrodes are shielded from disturbing magnetic fields by an exterior sheet metal member that is affixed to said tubular arm at a location between said electromagnet and the bulbous body portion of said envelope.

7. The short-arc electric discharge lamp of claim 5 wherein:

said movable ignitor assembly is aligned with the discharge gap and said arc-ignitor component comprises a bar of refractory metal;

said armature comprises a body of iron;

a helical spring is secured to the outermost end of said iron armature and maintains said armature in spaced-apart relationship with the side and end walls of said tubular arm; and

said ignitor assembly and ignitor bar are maintained in aligned relationship with the inner ends of said electrodes by guide means secured to the inner wall of said tubular arm at a location between said armature and the mouth of said tubular arm.

8. The short-arc electric discharge lamp of claim 5 wherein said electromagnet comprises a pair of independently energizable solenoids disposed in tandem encircling relationship with said tubular arm. 

